Method and apparatus for patch coating printed circuit boards

ABSTRACT

A method and apparatus for premetered &#34;patch&#34; coating discrete, incremental surfaces or substrates, such as printed circuit boards, integrated circuits and the like, with a pre-configured layer of a liquid in which a controlled volume per unit area of the liquid is applied to the substrate are disclosed. The liquid is dispensed from an applicator slot that is fluidly coupled to a liquid containing chamber. The volume of the liquid in the liquid containing chamber is varied in order to (1) sharply and distinctly start the coating &#34;patch&#34; by producing a pulse of liquid that flows out of the applicator slot to form a connecting bead of liquid coating on the coating surface and (2) sharply and distinctly terminate the coating &#34;patch&#34; by removing the bead of liquid connecting the applicator slot with the coated surface. The width of the coated &#34;patch&#34; is determined by the length of the applicator slot. Relative movement is provided between the applicator slot and the coating surface at least during the period between formation and termination of the bead of liquid in order to produce the desired &#34;patch&#34; length of liquid coating having predefined boundaries and a predetermined, uniform coating thickness.

BACKGROUND OF THE INVENTION

The present invention relates to liquid coating methods and apparatus ingeneral, and more particularly to a method and apparatus for premetered"patch" coating discrete, incremental surfaces or substrates, such asprinted circuit boards, integrated circuits, etc., wherein a premeteredvolume per unit area of liquid is applied to a surface with a liquidlayer "patch" having a pre-configured shape and a predetermined coatingthickness.

In the manufacture of printed circuit boards or integrated circuits itis often desirable to apply a liquid coating to the surface of thecircuit board or IC wafer, and it is critical that the thickness of thatwet coating be uniform across the surface of the board or substrate. Inthe case of photoresists or photo-imagable solder masks which aresolidified either by drying or by crosslinking with radiation, thethickness of the final solidified coating will generally be as uniformas that of the wet coating applied.

In manufacturing printed circuit boards, a photoresist is used totransfer the outline of the circuit into the copper surface of theboard. The term "photoresist" defines the dual functioning nature of thematerial. First it is a photo polymer whose chemical properties arechanged by exposure to ultraviolet radiation. That exposure is doneselectively through a mask outlining the circuit being defined. The dualfunctioning comes into play after developing the imaged photo polymer,where the soft unwanted areas are washed off the copper surface. Whatremains is a protective covering of hardened polymer only in those areasoutlined by the exposure mask. In one application, the circuit board isthen exposed to an etchant. The protective covering resists the etchingprocess so that only the copper surface left unprotected is etched away.When the developed resist is finally chemically stripped away, theprotected copper circuit lines underneath become the electricalconductors of the circuit board.

In the current manufacture of printed circuit boards, the chemicalprocesses of developing the imaged resist, etching the exposed copper,and stripping off the developed resist are all accomplished by exposingthe circuit board to a substantial oversupply of the developer, etchantor chemical stripper. This is usually done through a spray process thatalso provides agitation to enhance removal of the softened or dissolvedsurface material. These processes are costly, cumbersome and inefficientbecause by recycling the chemicals for economic reasons, the circuitboard's surface is exposed to previously reacted material. This reducesits chemical efficiency in reacting with the surface, increasing cycletime and reducing circuit definition. In addition it is difficult tomaintain the quality of the recycled material which causes its rate ofreaction with the surface to vary.

It is, accordingly, a general object of the invention to provide animproved coating method and apparatus.

It is a specific object of the invention to provide a method andapparatus for premetered "patch" coating discrete, incremental coatingsurfaces or substrates in which a controlled volume per unit area of aliquid is applied to the surface or substrate with a liquid layer"patch" having a pre-configured shape and coating thickness.

It is another object of the invention to provide a method and apparatusfor premetered "patch" coating discrete, incremental coating surfaces orsubstrates in which controlled volumes per unit area of liquids areapplied together in superposed relation to the surface or substrate witheach superposed liquid layer "patch" having a pre-configured shape andcoating thickness.

It is a feature of the invention that the coating method can be employedto coat various printed circuit board process liquids on printed circuitboards without requiring a substantial oversupply of each processliquid.

It is another feature of the invention that the apparatus provides forthe controlled application of liquids from a sharply defined start to asharply defined stop of the liquid coating or coatings applied to thesubstrate surface.

BRIEF DESCRIPTION OF THE INVENTION

The method and corresponding apparatus of the invention provide for theapplication of a controlled volume per unit area of a liquid coating toa discrete, incremental substrate with a premetered liquid layer "patch"thereon that has a four-sided shape and a predetermined coatingthickness. A source of liquid is fluidly coupled to a liquid containingchamber that in turn is fluidly coupled to an applicator slot having anapplicator slot exit aperture. With the substrate positioned inproximity to the applicator slot exit aperture, the coating "patch" isinitiated by producing a positive pulse of liquid that flows out of theapplicator slot exit aperture forming a bead of liquid coating andsending a controlled volumetric flow rate of the liquid through theapplicator slot. The positive pulse of liquid preferably is produced bysuddenly displacing a volume of the liquid in the liquid containingchamber. Once the liquid connecting bead is formed with the substrate,the controlled volumetric flowrate of the liquid issuing from theapplicator slot exit aperture combined with relative movement betweenthe applicator and the substrate apply the liquid coating to thesubstrate surface. Termination of the liquid coating bead preferably isachieved with a negative, disconnecting pulse that creates a momentaryvacuum in a portion of the liquid containing chamber which sucks thecoating liquid up into the applicator slot and breaks the connectingbead of liquid coating between the applicator slot exit aperture and thesubstrate surface.

BRIEF DESCRIPTION OF THE DRAWINGS

The objects and features of the present invention will best beunderstood from a detailed description of a preferred embodimentthereof, selected for purposes of illustration and shown in theaccompanying drawings in which:

FIG. 1 is a diagrammatic illustration of the liquid coating variables;

FIG. 2 is a schematic representation of a liquid coating apparatus;

FIG. 3 is another schematic representation of the coating apparatus ofFIG. 2 showing the positioned relationship between a printed circuitboard and the exit aperture of a coating applicator slot;

FIG. 4 is another schematic representation of the coating apparatus ofFIG. 2 showing the initial application of a bead of the liquid coatingon the printed circuit board;

FIG. 5 is another schematic representation of the coating apparatus ofFIG. 2 showing further application of the liquid coating to the printedcircuit board;

FIG. 6 is another schematic representation of the coating apparatus ofFIG. 2 showing termination of the application of the liquid coating tothe printed circuit board;

FIG. 7 is another schematic representation of the coating apparatus ofFIG. 2 showing the sealing of the applicator slot;

FIG. 8 is a schematic representation of a multilayer coating apparatusfor the simultaneous application of two liquid layers to a substrate;and,

FIG. 9 is a schematic representation of a process for manufacturing aprinted circuit board.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to FIG. 1, there is shown in diagrammatic form apremetered coating process. The process liquid can be coated onto thesurface of a printed circuit board be it photoresist, developer,etchant, chemical stripper, solder mask, or any other liquid chemicalusing a premetered coating system. The term "premetered coating" refersto a process in which a controlled volumetric flowrate of coating liquidis fed into a coating applicator that is spaced a distance x from thesurface of a substrate to be coated. As the substrate's surface passesby the applicator, the coating liquid issuing from the applicator slotis deposited onto the surface as a thin uniform layer.

The premetered process differs from a retained process such as dipcoating, spin coating, screen coating or roll coating in that theseprocesses expose the substrate's surface to an excess supply of coatingliquid. When that excess is removed, the amount retained on thesubstrate surface is a function of the coating fluid's rheologicalproperties, (viscosity, etc.) and the coating parameters.

Simply stated: in premetered coating a fixed volume is applied, whereasin retained coating excess volume is removed. With the premeteredprocess the liquid's viscosity does not determine the thickness of thewet coating deposited. As shown by the equation in FIG. 1, wet thicknessT, is simply a function of the volumetric flowrate V, divided by thecoating speed S, and the coating width W. Like all coating processes, ifthe coating is dried, the dried coating thickness t, is a function ofthe percent solids of the coating fluid.

With all retained coating processes, the coated wet thickness is afunction of the coating liquid's viscosity. Generally, a liquid'sviscosity will change if its percent solids changes either by loss ofthe coating fluid's solvent through evaporation or by over dilution ofthe coating liquid when solvent is back-added to compensate forevaporation losses. Therefore, in order to maintain the wet thickness ina retained coating process, the percent solids must be preciselymonitored and controlled. In addition, since viscosity is thermallydependent, the temperature of the coating liquid must also be preciselycontrolled.

With the premetered coating process, since there is no excess coatingliquid to be removed, the coating liquid can be confined in a closedsystem until it is applied to the substrate's surface. This prevents anyevaporation loss prior to coating. It also maintains the integrity ofthe coating liquid by minimizing its exposure to external contaminants.With the premetered process, wet thickness can be varied simply bychanging the volumetric flowrate, which can be precisely controlled. Forexample, if a volumetric flowrate of 1860 cm³ /min, combined with acoating speed of 610 cm/min and a coating width of 61 cm produces a wetcoating thickness of 0.05 centimeters, then simply by reducing thevolumetric flowrate to 93 cm³ /min, the wet thickness is reduced to0.0025 cm. (See FIG. 1). If the volume percent solids of the coatingliquid were 20%, then the calculated corresponding dry thickness wouldbe 0.01 cm for the 1860 cm³ /min volumetric flowrate, and 0.0005 cm forthe 93 cm³ /min volumetric flowrate. (See FIG. 1).

A schematic representation of the premetered "patch" coating process andapparatus is shown in FIGS. 2 through 8. Referring to FIG. 2, there isshown a coating apparatus constructed in accordance with the presentinvention and indicated generally by the reference numeral 10. Thecoating apparatus 10 has a coating applicator 12 comprising a chamber 14and applicator slot 16 supported by a positioning piston 18 having a gapstop adjusting screw 20. The coating liquid 22 which resides in a sealedreservoir 24 under a blanket of nitrogen gas 26 is piped through ametering pump 28 and a flexible connection 30 to an inlet valve 32mounted on the applicator 12. Also mounted on the applicator is adisplacement piston 34 connected to a displacement rod 36 which isinserted through the applicator wall 38 and an O-ring seal 40, accessingthe applicator chamber 14. Immediately below the applicator and incontact with the open applicator slot is a slot sealing unit 42 whichrides up and down on a shaft 44 connected to the slot seal piston 46.The slot sealing unit 42 cleans the applicator lips 48 prior to andafter application of the coating liquid 22 to a copper clad laminate 50(or substrate surface). At the same time, the slot sealing unit 42 sealsthe applicator slot exit aperture 51 that is defined by the applicatorlips 48.

The copper clad laminate 50 to be coated rests on top of a vacuum table52 that rides on linear bearings 54 so it can be moved smoothly past theapplicator positioned above the table. The vacuum table is fastened witha connecting link 56 to a drive chain 58 which goes around a drivesprocket 60. The drive sprocket 60 can be rotated at a preciselycontrolled rate by a precision drive motor (not shown). On top of thedrive assembly 62 are four micro-switches, A, B, C and D which are usedto signal the operating sequence.

In FIG. 2, prior to closing the inlet valve 32, the coating liquid ispumped from the sealed reservoir 24 into the liquid coating applicatorchamber 14 and down into the applicator slot 16. Any air coming into theapplicator chamber is bled off through an air bleed valve ("B.V.") 64.The slot sealing unit 42 is filled with a solvent similar to that in thecoating liquid and the applicator lips 48 are submerged beneath thesurface of the solvent in the slot sealing unit. This prevents thecoating liquid from drying out in the applicator slot, and washes offany coating liquid left on the applicator lips. Clean lips and slot aredesirable because any dried coating on the lips or slot will cause adisruption in the fluid flow resulting in a nonuniformity in thecoating.

A vacuum is drawn within the vacuum table and the copper clad laminatewhich covers the holes in the top of the table is pulled flat by thevacuum, up against the top of the table. The closure of switch "A" hasstopped the drive motor from rotating the drive sprocket and hasactuated the slot sealing piston to raise the slot sealing unit up intocontact with the coating applicator thereby sealing the applicator slotexit aperture 51.

When a coating cycle is initiated, an override button (not shown) ispressed which causes the drive motor to start rotating the drivesprocket. This moves the drive chain and through the connecting linkdrives the vacuum table and the copper clad laminate on top to the rightreleasing Switch "A" as shown in FIG. 3. The release of Switch "A"causes two actions to occur. First, the slot seal piston 46 retracts theslot sealing unit 42 to a position below the vacuum table. Secondly, thepositioning piston 18 strokes downward against the gap stop adjustingscrew 20 moving the applicator 12 downward to a predetermined coatinggap "x" formed between the applicator slot exit aperture 51 and thesurface of the copper clad laminate 50. This coating gap is equal to orless than one centimeter in contrast to curtain coating systems wherethe gap is significantly greater than one centimeter, such as the oneshown in U.S. Pat. No. 4,230,793, in which the gap is 10 centimeters.

As the vacuum table continues its rightward movement as viewed in FIG.4, it depresses Switch "B" which initiates three operations. In one ofthese operations, the displacement piston 34 is actuated causing thedisplacement rod 36 to move rapidly through the O-ring 40 and into thecoating liquid containing applicator chamber 14. The length of thedisplacement rod stroke is controlled by adjustable screw stop 37. Thedisplacement of the liquid caused by the sudden reduction in volume ofthe liquid in the chamber, produces a positive wave or positive pulse ofthe coating liquid that surges down the applicator slot, out theapplicator slot exit aperture defined by the applicator lips, and ontothe surface of the copper clad laminate, forming a connecting bead 66 ofcoating liquid between the applicator lips and the laminate. As shown inFIG. 4, simultaneously, the inlet valve opens and the metering pumpbegins to rotate, sending a controlled volumetric flowrate of thecoating liquid into and out of the applicator. Preferably, a pressuredifferential is established across the liquid coating bead 66 by meansof a bead vacuum chamber 68 to help keep the coating bead from beingpulled away from the applicator lips by the moving surface of theprinted circuit board. The bead vacuum chamber 68 is depicted only inFIG. 4 since its use is optional. These actions cause a sharp, uniformstart to the coating liquid being deposited on the printed circuitboard.

If a relatively large positive pulse is employed, the piston can beretracted (as described below in connection with FIG. 6) immediately tosuck-up the excess liquid without breaking the coating bead. Thisoscillatory action of the piston generates first a positive and then anegative pulse. The use of the oscillatory pulse sequence of positivethen negative, permits a larger pulse amplitude (volumetric displacementof the coating liquid) which insures proper connection of coating liquidbead with printed circuit board, especially when the coating speedand/or coating gap are increased and/or when the wet thickness of liquidis decreased.

The oscillatory pulses can be generated by single or multipledisplacement piston assemblies, such as, one or more pistons 34 anddisplacement rods 36. Furthermore, the location of the displacementpiston(s) can be varied from that shown in the Figures. Given the liquiddynamics, it can be seen that the piston(s) and its volumetricdisplacement chamber can be positioned upstream from the applicator 12and, preferably, downstream from the inlet valve 32 while stillproducing the desired positive and negative pulses.

If the sequence of the oscillatory pulsing of one of the displacementpiston assemblies is reversed from (positive pulse first, then negativepulse) to (negative pulse first, then positive pulse), then instead ofproducing a connecting bead, the bead is disconnected by first suckingthe liquid up into the applicator slot then expelling it out toward theapplicator slot exit aperture, but not sufficiently to reconnect thebead to the printed circuit board. In this way, the applicator slot iskept filled with liquid thereby eliminating air bubbles that could riseup the applicator slot and into the applicator chamber once the liquidflow through the applicator slot has been terminated.

Regulation of the volumetric displacement, the individual pulse durationand pulse amplitude and the time interval between positive and negativepulses allows a wide range of control for formation and removal of theconnecting bead of liquid coating.

Continuing with the sequence of operation shown in the drawings, as thevacuum table and the laminate move to the right, a dynamic wettingaction occurs whereby the liquid coming out of the applicator slot exitaperture is continuously applied to the surface of the laminate as auniformly thick layer 70 as shown in FIG. 5. The thickness of this layeris determined by the equation previously described and presented in FIG.1.

The application of the coating continues until the vacuum tabledepresses Switch "C". Upon closure of switch "C", the inlet valve 32closes, the metering pump 28 stops and the displacement piston 34rapidly retracts the displacement rod 36 back out of the applicatorchamber. A negative pulse is produced by retraction of the displacementrod which creates a momentary vacuum in the applicator chamber causingthe coating liquid to surge upward into the applicator slot as shown inFIG. 6. Simultaneously the positioning piston pulls the applicator backup against the gap stop as illustrated by the movement arrows in FIG. 6.These actions cause an abrupt break to the connecting bead of the liquidcoating leaving a clean, sharp end to the deposited liquid coating layeron the printed circuit board (or the substrate surface). Finally, inFIG. 7 when the vacuum table depresses Switch "D", the drive motor stopsrotating and the slot seal piston 46 raises the slot sealing unit 42 upinto contact with the coating applicator lips 48. The vacuum on thevacuum table 52 is released and the coated circuit board 50 can now beremoved for further processing.

It may be desirable at times to coat more than one layer in superposedrelationship on the substrate, e.g. a printed circuit board orintegrated circuit where each layer may be chemically different and mayprovide a different function. In order to eliminate the need to coat anddry each layer separately, the liquid layers can be applied to thesubstrate simultaneously using a multilayer premetered "patch" coatingapplicator shown schematically in FIG. 8. The same reference numeralsare used in FIG. 8 as were used in the previous Figures except thatletters "a" and "b" are employed to indicate the two separate coatingliquid systems. By carefully formulating the coating liquids, the layerswhen applied remain essentially separate and distinct. This "one pass"approach can offer substantial economic benefits in yield, productivityand capital expenditure.

It will be appreciated that the connecting bead of liquid coating can beformed by positive pulsing prior to the arrival of the printed circuitboard 50 beneath the applicator lips 51 as viewed in FIG. 3. In thiscase, the bead is first connected to the vacuum table 52 and then to theprinted circuit board. Similarly, the connecting bead can be terminatedeither by negative pulsing and/or sufficiently increasing the gapdistance x after the printed circuit board has passed the applicatorlips. If at any time between formation and termination of the connectingbead of liquid coating, the bead becomes discontinuous or disrupted,these problems can be corrected by means of a stabilizing pulse ofliquid either positive or oscillatory (positive, then negative),preferably oscillatory. The effect of the stabilizing pulse can be aidedby momentarily closing the inlet valve 32 during the duration of thepulse or by using a check valve (not shown) located upstream from theliquid coating chamber.

Although the printed circuit board 50 has been shown in the Figures as asingle printed circuit board for purposes of illustration, it should beunderstood that plural printed circuit boards can be positioned on thevacuum table 52, preferably in abutting relation, to permit the coatingof plural printed circuit boards in a "single pass". Alternatively, morethan one vacuum table can be employed to transport corresponding printedcircuit boards. The separation distance between vacuum tables, andtherefore the printed circuit boards, should be minimized to preventcoating discontinuities. However, any such coating discontinuities canbe corrected by means of a stabilizing pulse.

Referring to FIG. 9, Steps 1-17 present a pictoral schematic processflow diagram illustrating how the premetered "patch" coating process canbe used in the manufacturing of a printed circuit board from start tofinish. In Step 1 a liquid photoresist is coated onto the surface of acopper clad laminate using the premetered "patch" coating process andapparatus described in FIGS. 2-8. In Step 2, the coated laminate movesinto a dryer where the coating is solidified by driving off the solventusing heated air. After drying the laminate moves to an imaging stationStep 3, where the photoresist is selectively exposed through a mask. InStep 4, the imaged photoresist is coated with a developer liquid. InStep 5, using heat in combination with ultrasonic sound waves to agitatethe liquid coating, the unexposed resist is softened by the developerand loosened from the surface of the copper clad laminate. The circuitboard then moves to a wash station in Step 6 where the loose andsoftened unexposed photoresist is washed off. In Step 7, the laminate isthen dried before it goes to the next station.

In Step 8, an etching solution is coated onto the laminate. In Step 9again in combination with heat and ultrasonic sound, the etchantdissolves the copper surface off the laminate only where it is notprotected by the developed photoresist. The circuit board then moves toStep 10 where the dissolved copper and spent etchant are washed off, andin Step 11 the laminate is again dried thoroughly. In Step 12 a chemicalstripper is coated onto the laminate over the developed photoresist. InStep 13 using heat and ultrasonic sound, the chemical stripper softensand loosens the developed photoresist from the copper surface below. Thecircuit board then moves to Step 14 where the soft and loosenedphotoresist is washed away and in Step 15 the laminate is again dried.The circuit board then moves to an inspection station in Step 16 whereit is analyzed for dimensional accuracy and electrical continuity. Onceit passes the inspection it goes to a final operation where the circuitboard is flipped over to expose the other surface of the copper cladlaminate in Step 17. The laminate then begins to go through Steps 1-16of the cycle again to generate the circuitry on the other side of theboard. After passing inspection at Step 16 the second time, thecompleted double sided circuit board is removed for further processing.

By operating the circuit manufacturing process as a continuous line asshown in Steps 1-17, with the premetered "patch" coating processemployed in Steps 1, 4, 8 and 12, a tremendous increase in productivityis obtained over the current method of batch manufacturing. In additioncosts are substantially reduced due to less operating personnel and theyield is increased due to reduced manual handling of the circuit boards.The premetered "patch" coating process also reduces the quantity ofchemicals required because of their controlled and efficientapplication. In summary, the premetered "patch" coating process formanufacturing printed circuit boards offers a more cost effective,efficient and productive manufacturing process than those currentlyavailable.

Having described in detail a preferred embodiment of my invention, itwill now be apparent to those skilled in the art that numerousmodifications can be made therein without departing from the scope ofthe invention as defined in the following claims. For example, althoughthe positive and negative liquid pulses have been shown as beingproduced by a displacement system, these pulses also can be produced bymomentarily increasing or decreasing any existing volumetric flowrate ofthe liquid so that the net result of liquid flow is either out of orinto the applicator slot exit aperture. This can be accomplished bycontrolling the speed and rotational direction of the metering pump 28.

What I claim is:
 1. A method for applying a layer of a liquid with a controlled volume per unit area of the liquid to a printed circuit board comprising the steps of:A. fluidly coupling a source of the liquid to a liquid containing chamber, said liquid containing chamber being fluidly coupled to an applicator slot having an exit aperture so that both the chamber and applicator slot are filled with the liquid; B. moving a printed circuit board and the applicator slot exit aperture into proximity with each other; C. sending a controlled volumetric flowrate of the liquid from the source of the liquid to the liquid containing chamber and then through the applicator slot to create a uniform volumetric flowrate of liquid exiting from each point along the applicator slot exit aperture; D. generating a pulse to control the formation of a connecting bead of liquid coating between the applicator slot exit aperture and the printed circuit board, said connecting bead of liquid coating being formed prior to, at the same time as, or after the sending of the controlled volumetric flowrate of the liquid; and, E. relatively moving the printed circuit board and the applicator slot exit aperture with respect to each other to apply a uniform layer of the liquid with a controlled volume per unit area of the liquid on the printed circuit board.
 2. The method of claim 1 further comprising the step of sealing the applicator slot exit aperture after Step A and unsealing said applicator slot exit aperture before the liquid exits therefrom.
 3. The method of claim 1 wherein said applicator slot exit aperture is defined by applicator lips and further comprising the step of cleaning said lips before the liquid exits from the applicator slot exit aperture.
 4. The method of claim 1 wherein said layer of a liquid is applied to the printed circuit board so that the area of the layer is within the perimeter of the printed circuit board.
 5. The method of claim 1 wherein said layer of a liquid is applied to the printed circuit board so that at least a portion of the area of the layer is beyond the perimeter of the printed circuit board.
 6. The method of claim 1 wherein said relative movement commences prior to the formation of the connecting bead of liquid coating.
 7. The method of claim 1 wherein said relative movement commences at the same time as the formation of the connecting bead of liquid coating.
 8. The method of claim 1 wherein said relative movement commences after the formation of the connecting bead of liquid coating.
 9. The method of claim 1 wherein the printed circuit board is flattened to a planar configuration at least during Steps C, D and E.
 10. The method of claim 1 wherein the printed circuit board is in proximity with the applicator slot exit aperture so that they are separated by a distance X and further comprising the step of maintaining said separation distance X during Steps C, D and E.
 11. The method of claim 1 wherein the source of liquid is fluidly coupled to the liquid containing chamber to form a closed system therewith.
 12. The method of claim 1 wherein the formation of said connecting bead of liquid coating is controlled by generating a positive pulse of liquid that flows out of the applicator slot exit aperture and onto the printed circuit board.
 13. The method of claim 12 further comprising the step of generating a negative pulse of liquid that flows into the applicator slot exit aperture after generation of the positive pulse and without breaking said connecting bead of liquid coating.
 14. The method of claim 1 further comprising the step of establishing a differential pressure across the connecting bead of liquid coating so that the lower pressure is on the side of the liquid coating bead towards the uncoated portion of the printed circuit board during relative movement between the printed circuit board and the applicator slot exit aperture in Step E.
 15. The method of claims 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13 or 14 further comprising the step of terminating the flow of liquid to the printed circuit board by terminating the sending of the controlled volumetric flowrate of liquid from the source of liquid to the liquid containing chamber.
 16. The method of claims 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13 or 14 further comprising the step of terminating the flow of liquid to the printed circuit board by terminating the sending of the controlled volumetric flowrate of the liquid from the source of liquid to the liquid containing chamber and generating a negative pulse of liquid to momentarily create a vacuum in a portion of the liquid containing chamber whereby the liquid bead connecting the applicator slot exit aperture and the printed circuit board is removed from the printed circuit board.
 17. The method of claim 16 further comprising the step of generating a positive pulse of liquid that causes the liquid in the applicator slot to flow towards the applicator slot exit aperture after generation of the negative pulse and without reconnecting the bead of liquid coating with the printed circuit board.
 18. The method of claims 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13 or 14 wherein the printed circuit board is in proximity with the applicator slot exit aperture so that they are separated by a distance X and further comprising the step of terminating the contact of liquid with the printed circuit board by moving the printed circuit board relative to the applicator slot exit aperture so that the distance therebetween is greater than X.
 19. The method of claims 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13 or 14 wherein the liquid is a photoresist, said method further comprising the steps of drying and imaging or selectively curing the photoresist.
 20. The method of claims 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13 or 14 further comprising the steps of repeating Steps (A) through (E) n times, where n is at least
 1. 21. The method of claim 20 wherein the liquid is a photoresist the first time Steps A through E are performed and wherein the liquid is a developer the second time Steps A through E are performed, said method further comprising the steps of drying and imaging or selectively curing the photoresist, then performing Steps A through E for the second time and, thereafter, developing the imaged photoresist to soften and loosen the unwanted portions of the photoresist, washing the developed photoresist to remove the unwanted portions of the photoresist.
 22. The method of claim 20 wherein the liquid is an etchant the third time Steps A through E are performed, said method further comprising the steps of performing Steps A through E the third time and thereafter, dissolving the unprotected surface material of the printed circuit board, washing away the spent etchant and the dissolved surface material.
 23. The method of claim 20 wherein the liquid is a chemical stripper the fourth time that Steps A through E are performed, said method further comprising the steps of performing Steps A through E the fourth time and thereafter softening and loosening the remaining photoresist, washing away the softened and loosened remaining photoresist.
 24. The method of claim 1 further comprising the step of generating at least one additional pulse to control the formation of said connecting bead of liquid coating.
 25. The method of claim 24 further comprising the step of generating at least one additional pulse after formation of said connecting bead of liquid coating.
 26. The method of claim 21 further comprising the step of applying ultrasonic energy to the developer during the developing step.
 27. The method of claim 19 wherein the drying of the photoresist is accomplished at least in part by heating the printed circuit board prior to the formation of the connecting bead of the photoresist between the applicator slot exit aperture and the printed circuit board.
 28. The method of claim 19 wherein the selective curing of the photoresist is accomplished at least in part by heating the printed circuit board prior to the formation of the connecting bead of the photoresist between the applicator slot exit aperture and the printed circuit board.
 29. The method of claim 22 further comprising the step of applying ultrasonic energy to the etchant during the etching step.
 30. The method of claim 23 further comprising the step of applying ultrasonic energy to the chemical stripper during the stripping step.
 31. The method of claim 1 wherein the formation of said connecting bead of liquid is controlled by generating a negative pulse of liquid that flows into the applicator slot aperture.
 32. The method of claim 31 further comprising the step of generating a positive pulse of liquid that flows out of the applicator slot exit aperture after generation of the negative pulse.
 33. A method for applying a layer of liquid with a controlled volume per unit area of the liquid to a substrate comprising the steps of:A. fluidly coupling a source of the liquid to a liquid containing chamber, said liquid containing chamber being fluidly coupled to an applicator slot having an exit aperture so that both the chamber and applicator slot are filled with the liquid; B. moving a substrate and the applicator slot exit aperture into proximity with each other; C. sending a controlled volumetric flowrate of the liquid from the source of liquid to the liquid containing chamber and then to the applicator slot to create a uniform volumetric flowrate of liquid exiting from each point along the applicator slot exit aperture; D. generating a pulse to control the formation of a connecting bead of liquid coating on the substrate, said connecting bead of liquid coating being formed prior to, at the same time as, or after the sending of said controlled volumetric flowrate of the liquid; and, E. relatively moving the substrate and the applicator slot exit aperture with respect to each other to apply a uniform layer of the liquid with a controlled volume per unit area of the liquid on the substrate.
 34. The method of claim 33 further comprising the step of generating a negative pulse of liquid that flows into the applicator slot exit aperture after generation of the positive pulse and without breaking said connecting bead of liquid coating.
 35. The method of claim 33 further comprising the step of sealing the applicator slot exit aperture after Step A and unsealing said applicator exit slot aperture before the liquid exits therefrom.
 36. The method of claim 33 wherein said applicator slot exit aperture is defined by applicator lips and further comprising the step of cleaning said lips before the liquid exits from the applicator slot exit aperture.
 37. The method of claim 33 wherein said pulse is generated by displacing at least a portion of said connecting bead of liquid.
 38. The method of claim 33 wherein said pulse is generated by momentarily varying any existing flowrate of said liquid.
 39. The method of claim 33 wherein said layer of a liquid is applied to the substrate so that the area of the layer is within the perimeter of the substrate.
 40. The method of claim 33 wherein said layer of a liquid is applied to the substrate so that at least a portion of the area of the layer is beyond the perimeter of the substrate.
 41. The method of claim 33 wherein the substrate is in proximity with the applicator slot exit aperture so that they are separated by a distance X and further comprising the step of maintaining said separation distance X during Steps C, D and E.
 42. The method of claim 33 wherein said substrate includes at least one element of an integrated circuit.
 43. The method of claim 42 wherein said layer of a liquid is applied to the substrate so that the area of the layer is within the perimeter of the substrate.
 44. The method of claim 42 wherein said layer of a liquid is applied to the substrate so that at least a portion of the layer overlies at least a portion of said at least one element of the integrated circuit.
 45. The method of claim 42 wherein said layer is applied so that at least a portion of the area of the layer is beyond the perimeter of the substrate.
 46. The method of claim 42 wherein the liquid is a photoresist, said method further comprising the steps of drying and imaging or selectively curing the photoresist.
 47. The method of claim 33 wherein said relative movement commences prior to the formation of the connecting bead of liquid coating.
 48. The method of claim 33 wherein said relative movement commences at the same time as the formation of the connecting bead of liquid coating.
 49. The method of claim 33 wherein said relative movement commences after the formation of the connecting bead of liquid coating.
 50. The method of claim 33 wherein the substrate is positioned in a flattened configuration in proximity to the applicator slot exit aperture.
 51. The method of claim 33 wherein the source of liquid is fluidly coupled to the liquid containing chamber to form a closed system therewith.
 52. The method of claim 33 further comprising the step of establishing a differential pressure across the liquid coating connecting bead so that the lower pressure is on the side of the liquid coating connecting bead towards the uncoated portion of the substrate after continuation of relative movement between the substrate and the applicator slot exit aperture in Step E.
 53. The method of claims 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51 or 52 wherein the substrate is in proximity with the applicator slot exit aperture so that they are separated by a distance X and further comprising the step of terminating the contact of the liquid with the substrate by moving the substrate relative to the applicator slot exit aperture so that the distance therebetween is greater than X.
 54. The method of claims 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51 or 52 further comprising the step of terminating the flow of liquid to the substrate by terminating the sending of the controlled volumetric flowrate of liquid from the source of liquid to the liquid containing chamber.
 55. The method of claims 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51 or 52 further comprising the step of terminating the flow of liquid to the substrate by terminating the sending of the controlled volumetric flowrate of the liquid from the source of liquid to the liquid containing chamber and generating a negative pulse of liquid to momentarily create a vacuum in a portion of the liquid containing chamber whereby the liquid bead connecting the applicator slot exit aperture and the substrate is removed from the substrate.
 56. The method of claim 55 further comprising the step of generating a positive pulse of liquid that causes the liquid in the applicator slot to flow towards the applicator slot exit aperture after generation of the negative pulse and without reconnecting the bead of liquid coating with the substrate.
 57. The method of claims 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51 or 52 further comprising the steps of repeating Steps (A) through (E) n times, where n is at least
 1. 58. The method of claim 33 further comprising the step of generating at least one additional pulse to control the formation of the connecting bead of liquid coating on the substrate.
 59. The method of claim 58 further comprising the step of generating at least one additional pulse after formation of said connecting bead of liquid coating.
 60. The method of claim 33 wherein the formation of said connecting bead of liquid is controlled by generating a positive pulse of liquid that flows out of the applicator slot exit aperture.
 61. The method of claim 33 wherein the formation of said connecting bead of liquid is controlled by generating a negative pulse of liquid that flows into the applicator slot exit aperture.
 62. The method of claim 61 further comprising the step of generating a positive pulse of liquid that flows into the applicator slot exit aperture after generation of the negative pulse.
 63. The method of claim 37 wherein said portion of said connecting bead of liquid is displaced by impact with said substrate.
 64. The method of claim 33 wherein the substrate is a printed circuit board and the liquid is a photoresist, said method further comprising the step of selectively drying the photoresist at least in part by heating the printed circuit board prior to the formation of the connecting bead of the photoresist between the application slot exit aperture and the printed circuit board.
 65. The method of claim 33 wherein the substrate is a printed circuit board and the liquid is a photoresist, said method further comprising the step of selectively curing the photoresist at least in part by heating the printed circuit board prior to the formation of the connecting bead of the photoresist between the application slot exit aperture and the printed circuit board.
 66. A method for applying controlled volume per unit area of liquids to a printed circuit board comprising the steps of:A. fluidly coupling n sources of corresponding n liquids to corresponding n liquid containing chambers that are fluidly coupled to corresponding n applicator slots each having an exit aperture so that each liquid containing chamber and its corresponding applicator slot are filled with the corresponding liquid and with said n applicator slot exit apertures being located in parallel, adjacent relationship, where n is equal to or greater than 2; B. moving a printed circuit board and said n applicator slot exit apertures into proximity with each other; C. sending controlled volumetric flowrates of the n liquids from the sources of the liquids to the corresponding n liquid containing chambers and then through the corresponding n applicator slots to create a uniform volumetric flowrate of each n liquid exiting from each point along its corresponding applicator slot exit aperture; D. generating a pulse to control the formation of a connecting bead of liquid coating between said n applicator slot exit apertures and the printed circuit board with the connecting bead containing each one of the n liquids, said connecting bead of liquid coating being formed prior to, at the same time as, or after the sending of the controlled volumetric flowrates of n liquids; and, E. relatively moving the printed circuit board and the n applicator slot exit apertures with respect to each other to simultaneously apply to the printed circuit board n superposed liquid layers each with a controlled volume of its liquid per unit area thereon.
 67. The method of claim 66 further comprising the step of sealing the applicator slot exit apertures after Step A and unsealing said applicator exit slot apertures before the liquids exit therefrom.
 68. The method of claim 66 wherein each said applicator slot exit aperture is defined by a corresponding set of applicator lips and further comprising the step of cleaning each of said sets of applicator lips before the liquids exit from the applicator slot exit apertures.
 69. The method of claim 66 wherein said layers of n liquids are applied to the printed circuit board so that the area of each layer is within the perimeter of the printed circuit board.
 70. The method of claim 66 wherein said layers of n liquids are applied to the printed circuit board so that at least a portion of the area of at least one layer is beyond the perimeter of the printed circuit board.
 71. The method of claim 66 wherein the printed circuit board is flattened to a planar configuration at least during Steps C, D and E.
 72. The method of claim 66 wherein the printed circuit board is in proximity with the applicator slot exit apertures so that they are separated by a distance X and further comprising the step of maintaining said separation distance X during Steps C, D and E.
 73. The method of claim 66 wherein the source of each of said n liquids is fluidly coupled to the corresponding liquid containing chamber to form a closed system therewith.
 74. The method of claim 66 wherein the formation of said connecting bead of liquid coating is controlled by generating a positive pulse of at least one of said n liquids that flows out of its applicator slot exit aperture and onto the printed circuit board.
 75. The method of claim 74 further comprising the step of generating a negative pulse of at least one of said n liquids that flows into its applicator slot exit aperture after generation of the positive pulse and without breaking said connecting bead of liquid coating.
 76. The method of claim 66 further comprising the step of establishing a differential pressure across the connecting bead of liquid coating so that the lower pressure is on the side of the connecting bead of liquid coating towards the uncoated portion of the printed circuit board during relative movement between the printed circuit board and the applicator slot exit apertures in Step E.
 77. The method of claims 66, 67, 68, 69, 70, 71, 72, 73, 74, 75 or 76 further comprising the step of terminating the flow of n liquids to the printed circuit board by terminating the sending of the controlled volumetric flowrates of n liquids from the sources of liquids to the corresponding liquid containing chambers.
 78. The method of claims 66, 67, 68, 69, 70, 71, 72, 73, 74, 75 or 76 further comprising the step of terminating the flow of n liquids to the printed circuit board by terminating the sending of the controlled volumetric flowrates of n liquids from the sources of liquids to the corresponding liquid containing chambers and generating a negative pulse of liquid of at least one of said n liquids to momentarily create a vacuum in a portion of its liquid containing chamber whereby the liquid bead connecting the applicator slot exit apertures and the printed circuit board is removed from the printed circuit board.
 79. The method of claim 78 further comprising the step of generating a positive pulse of liquid of said at least one of said n liquids that causes said liquid in its applicator slot to flow towards its applicator slot exit aperture after generation of its negative pulse and without reconnecting the bead of liquid coating with the printed circuit board.
 80. The method of claims 66, 67, 68, 69, 70, 71, 72, 73, 74, 75 or 76 wherein the printed circuit board is in proximity with the applicator slot exit apertures so that they are separated by a distance X and wherein the connecting bead of liquid coating with the printed circuit board is broken by moving the printed circuit board relative to the applicator slot exit apertures so that the distance therebetween is greater than X.
 81. The method of claim 66 further comprising the step of generating at least one additional pulse to control the formation of said connecting bead of liquid coating.
 82. The method of claim 81 further comprising the step of generating at least one additional pulse after formation of said connecting bead of liquid coating.
 83. The method of claim 66 wherein said relative movement commences prior to the formation of the connecting bead of liquid coating.
 84. The method of claim 66 wherein said relative movement commences at the same time as the formation of the connecting bead of liquid coating.
 85. The method of claim 66 wherein said relative movement commences after the formation of the connecting bead of liquid coating.
 86. The method of claim 66 wherein the formation of said connecting bead of liquid is controlled by generating a negative pulse of at least one of said n liquids that flows into its applicator slot exit aperture.
 87. The method of claim 86 further comprising the step of generating a positive pulse of at least one of said n liquids that flows out of its applicator slot exit aperture.
 88. A method for applying n layers of liquids with a controlled volume per unit area of each liquid to a substrate comprising the steps of:A. fluidly coupling n sources of corresponding n liquids to corresponding n liquid containing chambers that are fluidly coupled to corresponding n applicator slots each having an exit aperture so that each liquid containing chamber and its corresponding applicator slot are filled with the corresponding liquid and with said n applicator slot exit apertures being located in parallel, adjacent relationship, where n is equal to or greater than 2; B. moving a substrate and the applicator slot exit apertures into proximity with each other; C. sending controlled volumetric flowrates of the n liquids from the sources of liquid to the corresponding n liquid containing chambers and then through the corresponding n applicator slots to create a uniform volumetric flowrate of each n liquid exiting from each point along its applicator slot exit aperture; D. generating a pulse to control the formation of a connecting bead of liquid coating on the substrate containing each one of the n liquids, said connecting bead of liquid being formed prior to, at the same time as, or after the sending of said controlled volumetric flowrate of the liquid; and, E. relatively moving the substrate and the n applicator slot exit apertures with respect to each other to simultaneously apply to the substrate n superposed layers of the n liquids each with a controlled volume per unit area of its liquid thereon.
 89. The method of claim 88 further comprising the step of generating a negative pulse of at least one of said n liquids that flows into its applicator slot exit aperture after generation of its positive pulse and without breaking said connecting bead of liquid coating.
 90. The method of claim 88 further comprising the step of sealing the applicator slot exit apertures after Step A and unsealing said applicator exit slot apertures before the n liquids exit therefrom.
 91. The method of claim 88 wherein each said applicator slot exit aperture is defined by a corresponding set of applicator lips and further comprising the step of cleaning each of said sets of applicator lips before the n liquids exit from the applicator slot exit apertures.
 92. The method of claim 88 wherein said pulse is generated by displacing at least a portion of said connecting bead of at least one of said n liquids.
 93. The method of claim 88 wherein said pulse is generated by momentarily varying any existing flowrate of said liquid.
 94. The method of claim 88 wherein said superposed layers of n liquids are applied to the substrate so that the area of the layers is within the perimeter of the substrate.
 95. The method of claim 88 wherein said superposed layers of n liquids are applied to the substrate so that at least a portion of the area of the layers is beyond the perimeter of the substrate.
 96. The method of claim 88 wherein said substrate includes at least one element of an integrated circuit.
 97. The method of claim 96 wherein said superposed layers of n liquids are applied to the substrate so that the area of the layers is within the perimeter of the substrate.
 98. The method of claim 96 wherein said superposed layers of n liquids are applied to the substrate so that at least a portion of the area of at least one layer overlies at least a portion of said at least one element of the integrated circuit.
 99. The method of claim 96 wherein said superposed layers of n liquids are applied so that at least a portion of the area of the layers is beyond the perimeter of the substrate.
 100. The method of claim 96 wherein said at least one of said n liquids is a photoresist and further comprising the step of drying and imaging or selectively curing the photoresist.
 101. The method of claim 88 wherein said relative movement commences prior to the formation of the connecting bead of liquid coating.
 102. The method of claim 88 wherein said relative movement commences at the same time as the formation of the connecting bead of liquid coating.
 103. The method of claim 88 wherein said relative movement commences after the formation of the connecting bead of liquid coating.
 104. The method of claim 88 wherein the substrate is positioned in a flattened configuration in proximity to the applicator slot exit apertures.
 105. The method of claim 88 wherein the source of each of said n liquid is fluidly coupled to the corresponding liquid containing chamber to form a closed system therewith.
 106. The method of claim 88 further comprising the step of establishing a differential pressure across the liquid coating connecting bead so that the lower pressure is on the side of the liquid coating connecting bead towards the uncoated portion of the substrate after continuation of relative movement between the substrate and the applicator slot exit aperture in Step E.
 107. The method of claims 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 100, 101, 102, 103, 104, 105 or 106 wherein the substrate is positioned at a distance X from the applicator slot exit apertures and further comprising the step of terminating the flow of n liquids to the substrate by moving the substrate relative to the applicator slot exit apertures so that the distance therebetween is greater than X.
 108. The method of claims 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 100, 101, 102, 103, 104, 105 or 106 further comprising the step of terminating the flow of n liquids to the substrate by terminating the sending of the controlled volumetric flowrate of n liquids from the sources of the liquids to their corresponding liquid containing chambers.
 109. The method of claims 80, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 100, 101, 102, 103, 104, 105 or 106 further comprising the step of terminating the flow of n liquids to the substrate by terminating the sending of the controlled volumetric flowrate of n liquids from the sources of the liquids to their corresponding liquid containing chambers and generating a negative pulse of liquid of at least one of said liquids to momentarily create a vacuum in a portion of its liquid containing chamber whereby the liquid bead connecting the applicator slot exit apertures and the substrate is removed from the substrate.
 110. The method of claim 109 further comprising the step of generating a positive pulse of liquid of said at least one of said n liquids that causes said liquid in its applicator slot to flow towards its applicator slot exit aperture after generation of its negative pulse and without reconnecting the bead of liquid coating with the the substrate.
 111. The method of claim 88 wherein the substrate is in proximity with the applicator slot exit apertures so that they are separated by a distance X and further comprising the step of maintaining said separation distance X during Steps C, D and E.
 112. The method of claim 88 further comprising the step of generating at least one additional pulse to control the formation of the connecting bead of liquid coating on the substrate.
 113. The method of claim 112 further comprising the step of generating at least one additional pulse after formation of said connecting bead of liquid coating.
 114. The method of claim 10, 41, 72 or 111 wherein the distance x is varied prior to step E.
 115. The method of claim 10, 41, 72 or 111 wherein the distance x is increased prior to step E.
 116. The method of claim 10, 41, 72 or 111 wherein the distance x is decreased prior to step E.
 117. The method of claim 88 wherein the formation of said connecting bead of liquid is controlled by generating a positive pulse of at least one of said n liquids that flows out of its applicator slot exit aperture.
 118. The method of claim 88 wherein the formation of said connecting bead of liquid is controlled by generating a negative pulse of at least one of said n liquids that flows into its applicator slot exit aperture.
 119. The method of claim 118 further comprising the step of generating a positive pulse of at least one of said n liquids that flows out of its applicator slot exit aperture.
 120. The method of claim 92 wherein said portion of said connecting bead of at least one said n liquids is displaced by impact with said substrate.
 121. The method of claim 88 wherein the substrate is a printed circuit board and at least one of the liquids is a photoresist, said method further comprising the step of selectively drying the photoresist at least in part by heating the printed circuit board prior to the formation of the connecting bead of the photoresist between the application slot exit aperture and the printed circuit board.
 122. The method of claim 88 wherein the substrate is a printed circuit board and at least one of the liquids is a photoresist, said method further comprising the step of selectively curying the photoresist at least in part by heating the printed circuit board prior to the formation of the connecting bead of the photoresist between the application slot exit aperture and the printed circuit board.
 123. A method for applying a layer of a liquid with a controlled volume per unit area of the liquid to an integrated circuit substrate comprising the steps of:A. fluidly coupling a source of the liquid to a liquid containing chamber, said liquid containing chamber being fluidly coupled to an applicator slot having an exit aperture so that both the chamber and applicator slot are filled with the liquid; B. moving an integrated circuit substrate and the applicator slot exit aperture into proximity with each other; C. sending a controlled volumetric flowrate of the liquid from the source of the liquid to the liquid containing chamber and then through the applicator slot to create a uniform volumetric flowrate of liquid exiting from each point along the applicator slot exit aperture; D. generating a pulse to control the formation of a connecting bead of liquid coating between the applicator slot exit aperture and the integrated circuit substrate, said connecting bead of liquid coating being formed prior to, at the same time as, or after the sending of the controlled volumetric flowrate of the liquid; and, E. relatively moving the integrated circuit substrate and the applicator slot exit aperture with respect to each other to apply a uniform layer of the liquid with a controlled volume per unit area of the liquid on the integrated circuit substrate.
 124. A method for applying controlled volume per unit area of liquids to an integrated circuit substrate comprising the steps of:A. fluidly coupling n sources of corresponding n liquids to corresponding n liquid containing chambers that are fluidly coupled to corresponding n applicator slots each having an exit aperture so that each liquid containing chamber and its corresponding applicator slot are filled with the corresponding liquid and with said n applicator slot exit apertures being located in parallel, adjacent relationship, where n is equal to or greater than 2; B. moving an integrated circuit substrate and said n applicator slot exit apertures into proximity with each other; C. sending controlled volumetric flowrates of the n liquids from the sources of the liquids to the corresponding n liquid containing chambers and then through the corresponding n applicator slots to create a uniform volumetric flowrate of each n liquid exiting from each point along its corresponding applicator slot exit aperture; D. generating a pulse to control the formation of a connecting bead of liquid coating between said n applicator slot exit apertures and the integrated circuit substrate with the connecting bead containing each one of the n liquids, said connecting bead of liquid coating being formed prior to, at the same time as, or after the sending of the controlled volumetric flowrates of n liquids; and, E. relatively moving the integrated circuit substrate and the n applicator slot exit apertures with respect to each other to simultaneously apply to the integrated circuit substrate n superposed liquid layers each with a controlled volume of its liquid per unit area thereon. 